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Positron in a magnetic field

  1. May 8, 2016 #1
    1. The problem statement, all variables and given/known data
    A positron moves in a circular path of radius R due to a uniform magnetic field of strength B applied perpendicular to the plane of the circle. If B is varied, which of the following best represents a graph of the kinetic energy of the positron as a function of B so that the positron maintains the same radius R.

    2. Relevant equations

    3. The attempt at a solution
    KE = 1/2MV^2

    Rearranging first equation, RqvB =mv^2, then multiply each side by 2

    2RqvB = KE

    Here i thought that KE is proportional to B, but v remains a variable that depends on KE. How do create a relationship between B and KE?
  2. jcsd
  3. May 8, 2016 #2


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    Try using qvB=mv2/R to get an expression for v.
  4. May 8, 2016 #3
    Wow. I don't know how I messed that up. Graph is quadratic. Thanks for your help!
  5. May 8, 2016 #4


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    Homework Helper
    Gold Member

    Good work.
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